Utilization of low-temperature tars



Jan. 10, 1961 M. B. DELL |-.rAL

UTILIZATIQN QF' LOW-TEMPERATURE TARS Filed Jan. 10, 1958 United States Patent() UTILIZATIDN F LOW-TEMPERATURE TARS Manuel Benjamin Dell, New Kensington, Pa., and Vernon M. Stowe, Caseyville Township, St. Clair County, Ill., assignors to Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Filed Jan. 10, 1958, Ser. No. 708,211

Claims. (Cl. 208-2) 'tars from which valuable products might be obtained. flhe present invention is directed to the utilization of such 'low-temperature tars and to the hydrogen-treatment of fractions thereof to produce refined hydrocarbon liquids suitable for use as solvents.

`The term hydroreining, as used herein, refers to the catalytic treatment of low-temperature tar fractions comprising, at least in part, organic compounds containing combined heteroatoms such as sulfur, nitrogen and oxygen, at high temperatures and medium pressures in the presence of hydrogen to produce the corresponding hydrocarbons, and removable hydrogen compounds of the heteroatoms such as hydrogen suliide, water and ammoniacal substances. Saturation of oleiins generally accompanies the removal of the heteroatoms, and other reactions may incidentally occur such as cyclization, dehydrogenation and dealkylation.

The term low-temperature carbonization, as used herein, refers to a process for the carbonization of bituminous materials at temperatures lower than about 1300 F. Representative of such a process is that described by V. F. Parry in U.S. Patent 2,773,018 and in Drying and Carbonizing Fine Coal in Entrained and Fluidized State, Bureau of Mines Report of Investigations 4954, U.S. Department of Interior, dated April i953.

The term low-temperature tar, as used herein, refers to tars produced by low-temperature carbonization of peat, brown coal, lignite, sub-bituminous or bituminous coals. Such tars are generally oily, tarry organic masses ranging from viscous liquids to soft semi-solid materials at room temperature and may contain small quantities of char, ash or other inert material, dissolved gases and water.

A typical analysis of low-temperature tar obtained by carbonization of Texas lignite at 946 F. utilizing the Parry Process, supra, is shown in Table l below:

TABLE 1 Analysis ofcrude tar .Specific gravity, 60/ 60 F 0.9867

`Ash-weight percent 0.35

ice

Moisture, weight percent 2.9 C-I (quinoline-insolubles), weight percent 1.41 Distillation ASTM D20-52, dry basis, weight percent: l

To 170 C. 2.2 170235 C. V18.4 23S-270 C. 12.6 270300 C. 12.8 300 C. to decomposition temperature 31.3 Residue at decomposition temperature 19.7 Loss 3.0 Decomposition temperature, C 329 Analysis of distillate, vol. percent:

Tar bases 4.3 Tar acids 23.9 Neutral oil 71.8

Hydrocarbon types 1:

Saturates 14 Olens 40 Aromatics 46 1 Method disclosed in article by G. U. Dinneen et al., Shale Oil Naphthas: Analysis of Small Samples by Silica Gel Adsorption Method, Analytical Chemistry, vol. 19, p. 992 (1947).

Low-temperature carbonization is generally favored for the production of large quantities of tar as compared to high-temperature processes, thus permitting recovery of considerably greater amounts of tar oils. However, considerable differences exist in the nature of the tars. Hightemperature tars are completely aromatic and about percent consists of 3 to 7 ring aromatic compounds with molecular Weights up to 400, the remainder consisting 0f higher molecular weight carbonaceous compounds; in addition, the percentage of phenolic constituents is only about 5 to l2 percent, but substantially all vof these are low-boiling tar acids. Low-temperature tar is only partially aromatic, i.e. about 10-45 percent. It contains relatively large quantities of phenolic constituents, ranging from 20 to 45 percent of the tar; however, these are about evenly distributed in the valuable low-boiling phenolic range and in the higher boiling fraction. i

The by-product recovery treatment of such tars may involve a distillation process to recover low-boiling oils from which tar acids are recovered. These phenolic constituents are usually a readily marketable commodity ,and

constitute a definite enhancement to the value of the lthe substantially complete utilization of low-temperaturek tars.

Another object is to provide a method for the treat- 4ment of low-temperature tars whereby refined hydrocarbon liquids and other valuable products are obtained. i y

It is also an object to provide a method wherein lowvtemperature tars are utilized to produce hgh-qualitycke suitable for carbon electrodes and other valuable products.

A further object is to provide a method for cracking the high-boiling tar acids in low-temperature tars tothe more valuable low-boiling tar acids.

Further-objects and advantages of the present invention will be evident from theattached drawing and following `detailed description.

It has now been found that low-temperature tars may be substantially completely utilized by a method in which the tar, or a fraction thereof, is thermally decomposed into coke suitable for carbon electrodes, gas and condensible oils comprising at least in part organic cornpounds containing combined heteroatoms such as sulfur, nitrogen and oxygen. The condensible oils, or fractions thereof, are then catalytically treated with hydrogen at high temperatures and medium pressures to convert the `heteroatorn-containing organic components into hydro carbons and easily removable hydrogen compounds of the heteroatorns, thus removing sulfur', nitrogen and oxygen; simultaneously, olenic material is saturated.

More particularly, the thermal decomposition takes place at a pressure between Yatmospheric and 100 pounds per square inch and at a temperature of about 375 C. Ato` 475 C. The hydroreining conditions include a temperature between 425 C. and 620 C. a pressure between 100 and 1000 p.s.i.g., a liquid hourly space velocity between 0.25 and 4.0, and a hydrogen feed rate between 1000 and 6000 cubic feet per barrel of feed. Preferably, .the whole or crude tar is initially distilled to recover phenolic oil prior to the thermal decomposition; it is also desirable to fractionate the condensible oils from the thermal decomposition so as to recover a second phenolic `oil which has resulted from cracking of the higher boiling constituents, the balance of the condensible oils or middle oil being used as the feedstock for the hydroreining operation. These phenolic oils are desirably processed to recover tar acids and tar bases, leaving a'neutral oil which also may be hydrorelined either separately or in admixture with the middle oil. Similarly, the phenolic oils may be caustic-washed only to recover the tar acids alone.

The terms low-temperature tar feedstock or tar feedstock, as used herein, refer to crude or whole lowtemperature tars, or to fractions thereof, such as the residues upon topping, or distillates.

The term phenolic oil, as used herein, refers to a tar distillate relatively rich in valuable phenolic constituents, such as phenol, cresols, xylenols, and ethyl phenols. It is preferred to use about 235 C. as the end point for this distillate, although variations may be made dependent upon the compounds desired in this fraction.

The term middle oil, as used herein, refers to a tar distillate boiling above the phenolic oil range.

The term tar distillate, as used herein, refers to any distillate from low-temperature tars or from tars formed in the thermal treatment of low-temperature tar, and may encompass phenolic oil, or middle oil, or both.

For a more detailed description, reference is made to the accompanying drawing, which is a diagrammatic owsheet illustrating an embodiment of the invention.

Low-temperature tar 2 is subjected to distillation in still 4 to recover phenolic oil 6 and leaving a residue 8. The residue 8 is subjected to thermal decomposition in retort 10 to yield gas 12, green coke 14 and condensible oils or condensate 16 which is fractionated in column 18 into phenolic oil 20 and middle oil 22. The middle oil 22 is then subjected to a hydrorening treatment in reactor 24 wherein it is treated with hydrogen or hydrogen-rich gas 26 to remove undesirable combined heteroatoms such as sulfur, nitrogen and oxygen, as well as to saturate olefinic constituents. The resultants are liquid product 28 and an off-gas 30 which is desirably processed in the hydrogen purification plant 32 to recover and/or make hydrogen or hydrogen-rich gas which then may be recycled as the reactant gas 26. A portion of the condensate 16, or middle oil 22, is preferably recycled and admixed with the residue 8 prior to the retort 10.

.aflezen The liquid product 28 is a refined partially aromatic oil, substantially free from noxious impurities, whichmnqay be used as a solvent. The liquid product is preferably fractionated in the column 34 into several fractions and a relatively high-boiling residue 36, which may be recycled for further processing in the reactor 24.

The higher-boiling fractions from the column 34 may desirably be subjected to a further refining step, such as by treatment with a solution of sulfuric acid or by percolation through clays.

The phenolic oil 6 is desirably subjected to a conventional treatment 38 to recover the tar bases 40, which treatment may be of the type utilizing dilute acid, and to a second treatment 42 to remove the tar acids 44, such as by washing with caustic solution or solvents, leaving a lowboiling neutral oil 4,6. The phenolic oil 20 from column 18 is also rich in low-boiling tar acids and tar bases which have resulted from the cracking of highboiling constituents in the retort 10, and these are conveniently recovered in extraction plants such as 38 and 42.

The neutral oil 46 is conveniently processed in the reactor 24 in order to refine it to valuable solvents, separately or in admixture with the middle oil, or it may be used without further treatment, if so desired.

The green coke 14 is desirably calcined in the retort 46 at temperatures above 1000 C. to prepare a highgrade calcined coke 48 suitable as an aggregate for carbon electrodes.

The apparatus for effecting the thermal decomposition may be of any type capable of affording the condition of temperature and pressure herein described. A delayed coker is preferably employed, although other types of coking apparatus, such as a pot still, may be satisfactorily utilized.

Generally, the temperature of the thermal decomposition is between 375 C. and 475 C. and preferably between 380 C. and 420 C. The pressures employed may vary between atmospheric and pounds per square inch. The pressure selected will depend largely upon the character of the feedstock, but about 40 to 60 pounds per square inch is preferable.

A portion of the condensible oils, such as the middle oil fraction, may be recycled and mixed with the tar feedstock prior to the preheater. By so doing, especially in the case of topped tar, the feedstock is more easily transported and premature coking is substantially eliminated. Generally, this recycle ratio may be between 0.3 and 3.0 times the feedstock, and preferably between 0.5 and 1.5.

The ash content of the coke produced by the process will be dependent upon that of the feedstock. Especially for the production of anodes for electrolytic reduction cells, it is desirable that the coke contain as little ash as possible and generally less than about 0.8 percent. Thus when employing low-temperature tars which usually contain considerable quantities of ash, it has been found desirable to reduce the solids contained in the feed tar prior to the thermal decomposition. For this purpose, several methods may be employed such as, for example, those disclosed in U.S. Patents 2,631,982 to Donegan and 2,774,716 to Kulik.

Temperatures between about 425 C. and 620 C. are employed for the hydrogen treatment, the specific tempertures depending upon the nature of the low-temperature tar fraction treated. Temperatures above 620 C. tend to reduce the yield of liquid product, whereas temperatures below 425 C. do not effect sufficient removal of the heteroatoms. Generally, it is preferred .to use temperatures between 425 C. and 510 C. for neutral oil boiling below about 235 C., and temperatures between 510 C. and 540 C. for middle oil.

The hydrorening proceeds satisfactorily at total pressures between 100 and 1000 pounds per square inch gauge. Pressures above 1000 p.s.i.g. cause excessive cracking of the molecules and hydrogenation of the arofnatic nuclei, While pressures below 100 p.s.i.g. result in increased deposits of carbonaceous materials on the catalyst. Generally, a pressure between 500 and 800 p.s.i.g'. is preferred for treatment of both neutral oil and middle oil.

Ihe liquid hourly space velocity may be between 0.25 and 4.0 volumes per volume of catalyst per hour. Generally, lower space velocity rates decrease the liquid product yield, whereas higher rates do not provide sucient purification of the feed. Preferably a rate of between about 0.5 and 1.3 is employed for treatment of all tar fractions.

The hydrogen feed should be in excess of stoichio-metric requirements as amounts less than this do not provide suicient purification, and quantities above 6000 cubic feet per barrel become prohibitive from both cost and handling standpoints. Generally, about 3000 cubic feet per barrel has been preferred for treatment of the various tar fractions.

The catalyst employed may be any of the contact agents generally employed to promote desulfurization. Found especially suitable were oxides of cobalt and molybdenum on alumina, molybdenum oxide on alumina, and oxides of nickel and tungsten on alumina. Specifically, the follow- .ing catalysts have been satisfactorily employed: 2.55 per- `cent cobalt oxide and 15.45 percent molybdenum oxide on alumina; 5 percent cobalt oxide and l1 percent molybtdenum `oxide on alumina; l1 percent molybdenum oxide von alumina; 3 percent cobalt oxide on alumina; and 4 per- Icent nickel oxide and 7 percent tungsten oxide on alumina.

In accordance with this invention, crude or whole lignite low-temperature tar, as substantially described in Table 1, was distilled to recover phenolic oil. Data on this distillation are shown in Table 2 below:

A low-temperature lignite tar residue, substantially as described in Table 2, was thermally decomposed in a delayed coker to obtain green coke, process gas and condensate as shown in Tables 3 and 4.

TABLE 3 Thermal decomposition Conditions:

Temp., C. 425 Pressure, p.s i g 50 Product yields:

Coke, green, wt. percent of feed 26.1 Gas, cu. ft. per lb. of feed 1.18 Condensate, wt. percent of feed 62.8 Phenolic oil (to 235 C.), vol. percent of condensate 32.0 Middle oil (over 235 C.), vol. percent of of condensate 68.0

TABLE 4 Product analysis Gas, mol percent:

Hydrogen .4.9. Methane 476.3 Ethane 15.4 Propane 7.7 Ethylene 2-5 Propylene 3.8 Carbon monoxide 5.6 Carbon dioxide 5.7 Others 7.1 Condensate composition, vol. percent:

Tar bases 2.6 Tar acide 18.7 Neutral oil 78.7

Hydrocarbon types, vol. percent:

Saturates 25 Aromatics 40 Olens 35 Condensate distillation, ASTM D-86:

Initial, C 51 10 ml 167 20 ml 207 30 ml 231 40 ml 251 50 ml 260 60 mi 284 70 ml 331 85.8 ml 337 Decomposition, C 337 Residue, percent 10.8

The middle oil from the thermal decomposition described in Table 3 was hydroretined in accordance with the present invention; neutral oil obtained by extraction of the tar acids and tar bases of the phenolic oil described in Table 3 was also hydrorelined. The catalyst employed was one containing 2.55 percent cobalt oxide and 15.45 percent molybdenum -oxide on alumina. Analyses of the feedstocks, data on hydrorefining conditions and analyses of the hydroretned products are given in the following tables.

TABLE 5 Feedstock analysis vA B Type of Feedstoek Middle Neutral Y Oil Oil specific gravity, eos/60 F o. 9365 Refractive index, l:120D 1. 5168 Sulfur, wt. percent 0, 81 0.83 Nrtrogeu, wt. percent O. 40 Nil Mixed anllne point, C 52. 8 47. 2 Distillation, ASTM D15841, C.:

Initial boiling point 109 72 5% 230 117 10% 239 131 20% 249 151 30% 258 166 40% 268 179 50% 277A 191 60% 289 203 70% 301 215 316 227 90% 337 246 91% 339 95% 262 98% 281 TABLE 6 Hydrorefnng conditions 4 Temperature, C 511 491 Pressure, p.s..g 500 i500.` Liquid hourly space velo 1.0 l. 0 H2, cu. ft. per bbl. of feed 3,000 3.000

TABLE 7 Reformatie products Product yield, vol. percent feed:

' Organic 91 94 Inorganic 7. 4 4. 4 Gas;

Hz consumed, cu. it./bbl---.: 1,096 753 H: recoverable from methane 1n cti-gas, cu.

ft. bl-.`. 1,150 688 Organic product:

Specific gravity, 60/60 F 0. 8693 0. 7959 Refractive index '112D.- 1. 5018 1. 4524 Sulfur, percent 0.050 0. 010 Nitrogen, percent 0.09 1\.'1l Mixed aniline point, C.- 47 53 Kauri butanol. 61. 5 48. 8

The reformate or hydroreiined product is a partially aromatic oil which may be distilled into several fractions suitable as` commercial solvents. The properties of these several fractions, as given in Table 8, indicate good solvent characteristics by reason of their aromaticity and low sulfur and nitrogen contents. The fractions boiling above 93 C. were washed with 70% sulfuric acid.

Having thus described the invention, we claim:

1. In the utilization of low-temperature tars to prepare electrode-quality coke, reiined hydrocarbon liquids 'suitable as solvents and other valuable productsQthc method comprising distilling low-temperature tar to re- .cover phenolic` oil; thermally decomposing the. residue from said phenolicoil distillation at a temperature be; tween 375 C. and 475 C. and a pressure between atmospheric and 100 pounds per square inch to convert said residue into coke, gaseous products, and condensiblc. oils including phenolic oil and middle oil, said condensible oils being comprised, in part, of organic compounds containing combined heteroatoms; recycling a portion of condensible hydrocarbons in admixture with said residue in an amount between 0.3 and 3.0 to l prior to said thermal decomposition step; extracting phenolic constituents from said first-mentioned and second-mentioned phenolic oils; hydroreiining said middle oil by catalytic treatment with hydrogen at a temperature between 425 C. and 620 C., a pressure between 100 and 1000 pounds per square inch and a liquid hourly space velocity between 0.25 and 4.0, thereby obtaining rened hydrocarbon liquidssuitable as solvents.

2. The method in accordance with claim 1 in which TABLE 8 Solvent data Fraction, C Below 93 93-135 135-179 179-216 216-288 288- Decgmp. A. B A. B A B A B A B Yield, vol. percent, hydroretned l organic product- 6. 7 13. 3 9. 1 17. 1 11. 7 2714 12.0A 23. 2- 40A 5 1?. 2 16.0 Speclc gravity, 60/60 0. 6814 0. 7763 U. 7417 0.8224 0. 7938 0.8592 0. 8291 0. 8963 0. 8612 0. 9159 Mixed anllilie point, C l 36 0 1 64. 4 45. 56 57. 78 38. 89 51. 11 39. 44 50.00 43. 33 52. 22 56. 1l Kaurl butanol 35. 7 58. 7 43. 5 68.0 49. 1 65.0 51A 0 59. 1 52, 0 42. 5 Sulfur, percent Nil 0.01 Nil O. 01 Nil 0. 03 Nil 0.09 0.003 0. 08 Refractive index, n2D 1 4125 1. 3965 1.4403 1. 4160 1. 4645 1. 4458 1. 4855 1. 4660 1. 5115 1. 4879 1. 5265 1 straight munie point, c,

'Ihe green coke was calcined at atemperature of about 40 the oil from which the phenolic constituents are ex- 1200ci F. for 270 hours. The properties of the calcined material and of anodes prepared therewith were determined, comparison determinations being made for commercially available petroleum coke. As evidenced by the data in Table 9, the coke made in accordance with the present invention produces anodes of greatly irnproved resistivity; the baked apparent density is superior, and the sulfate reactivity is in the acceptable range and substantially equivalent to that of petroleum coke.

tracted is also hydroreiined.

3. The method in accordance with claim 2 in which the oil remaining after extraction of the phenolic constituents is hydrorened in admixture with the middle 45 Oil.

4. The method in accordance with claim 1 in which the coke is calcined at a temperature above l000 C. `to produce an electrodequality aggregate.

5. In the utilization of low-temperature tars` to pre- 1 Cylindrical anodes made with 110 C. softening point coke-oven pitch.

2 Great Lakes Carbon Company, Procedure No. C-12A 2 The anode is weighed dry, thensoaked for 24 hours in water containing few drops of a detcrgelt solution'. 'It is suspended in 'Water and weighed; then li: ls removed, dried with a towel and weighed while wet. The dlterence between the weight in water and wet Weight is determined and'then this'gure is difvidcdlnto the dry Weight to give the baked apparaat deisity;

4 A current of known amnerage is passed through a cylindrical anode; and a set of probes is usci to determine the voltage drop along the longitudinal axis. calculated by the formula: (E) (A) p*to (D) 'eliereV p-resistlvlty 1u ohm-inches E=average voltage drop across probes A=crossaseetlonal area of sample (square inches) I =currer1t passed through samples (amperes) D=dlstance between probes (inches) Reslstlvlty ls then 5 Sulfate ,reactivity ls'thelloss in welghtof a carbon specimen, 1 inch in diameter by M inch, when irnmersei in` molten sodiumrsulfate at 960 C measure of the reactivityoi process.

Itis considered an excellent ein abath for the production of aluminum by the'Hall pare electrode-quality coke, rened hydrocarbon liquids suitable as solvents and other valuable products, the method comprising distilling low-temperature tar to recover phenolic oil; thermally decomposing the residue from said phenolic oil distillation at a temperature between 375 C. and 475 C. and a pressure between atmospheric and 100 pounds per square inch to convert said residue into coke, gaseous products, and condensible oils including phenolic oil and middle oil, said condensibie oils being comprised, in part, of organic compounds containing combined heteroatoms; recycling a portion of condensible hydrocarbons in admixture with said residue to said thermal decomposition step; extracting phenolic constituents from said first-mentioned and second-menby catalytic treatment with hydrogen thereby obtaining refined hydrocarbon liquids suitable as solvents.

References Cited in the le of this patent UNITED STATES PATENTS OTHER REFERENCES Eglo et al.: Cracking of Low Temperature Coal Tar by Dubbs Process, 1926, Universal Oil Products Comtioned phenolic oils; and hydrorening said middle oil 15 P21115', ChicagO, Illinois 

1. IN THE UTILIZATION OF LOW-TEMPERATURE TARS TO PREPARE ELECTRODE-QUALITY COKE, REFINED HYDROCARBON LIQUIDS SUITABLE AS SOLVENTS AND OTHER VALUABLE PRODUCTS, THE METHOD COMPRISING DISTILLING LOW-TEMPERATURE TAR TO RECOVER PHENOLIC OIL; THERMALLY DECOMPOSING THE RESIDUE FROM SAID PHENOLIC OIL DISTILLATION AT A TEMPERATURE BETWEEN 375*C. AND 475*C. AND A PRESSURE BETWEEN ATMOSPHERIC AND 100 POUNDS PER SQUARE INCH TO CONVERT SAID RESIDUE INTO COKE, GASEOUS PRODUCTS, AND CONDENSIBLE OILS INCLUDING PHENOLIC OIL AND MIDDLE OIL, SAID CONDENSIBLE OILS BEING COMPRISED, IN PART, OF ORGANIC COMPOUNDS CONTAINING COMBINED HETEROATOMS; RECYCLING A PORTION OF CONDENSIBLE HYDROCARBONS IN ADMIXTURE WITH SAID RESIDUE IN AN AMOUNT BETWEEN 0.3 AND 3.0 TO 1 PRIOR TO SAID THERMAL DECOMPOSITION STEP; EXTRACTING PHENOLIC CONSTITUENTS FROM SAID FIRT-MENTIONED AND SECOND-MENTIONED PHENOLIC OILS; HYDROREFINING SAID MIDDLE OIL BY CATALYTIC TREATMENT WITH HYDROGEN AT A TEMPERATURE BETWEEN 425*C. AND 620*C., A PRESSURE BETWEEN 100 AND 1000 POUNDS PER SQUARE INCH AND A LIQUID HOURLY 